U.S. Pat. No. 6,537,470 B1 discloses a process for rapidly filling fibrous preforms and/or rigid, porous bodies with high viscosity resin or pitch. The process described in U.S. Pat. No. 6,537,470 is referred to as resin transfer molding (RTM). RTM processing is suitable for impregnating single or multiple porous bodies placed in a mold. The process may use a fibrous preform or rigid porous body, which is placed into a mold matching the desired part geometry. A resin is injected into the mold at high temperature and pressure. The mold is constructed from two mating pieces fitted to form one or more mold cavities. A gate fitted with a nozzle is set into one of the mold pieces, and a valve admits resin or pitch into the gate area. Venting or vacuum can be applied to the mold. The mold itself is held in a hydraulic press and an extruder is employed to supply the molten resin or pitch to the mold.
Resin transfer molding processing reduces densification costs in the manufacture of carbon-carbon composites. Because the high pressures used in RTM processing can destroy soft preforms, however, current processing includes a step of hardening/toughening the preforms using chemical vapor densification (CVD) prior to RTM densification.